Prince Eleri was one of several sons
of King Dingat - who ruled the
old territory of the Selgovae tribe in what is now Southern Scotland - and
his wife, St. Tenoi daughter of King Lot Luwddoc
(of the Host) of Gododdin. The family was probably expelled from
the region during King Edwin
of Northumbria's reign of terror in the North around AD 620. They
seem to have settled in the Bryn Buga (Usk) area of Gwent, when Eleri was
still a young man. His father entered the church and his five sons
were thus influenced to do likewise, although Eleri had started on this
road several years before, having been sent to study at Llanelwy (St.
Asaphs) in North Wales under St. Asaph.

It was probably
after his father's death that Eleri moved on to found the church at
Gwytherin in Rhufoniog (Gwynedd); for he took his, apparently widowed,
mother with him. It was here
that he welcomed his cousin's daughter, St.
Gwenfrewy (Winifred), when she was trying to start up a nunnery in
North Wales. She soon established a double monastery in the
village, with St. Eleri as Abbot for the monks and St. Tenoi as Abbess for
the nuns. Eleri survived Gwenfrewy by a number of years, having buried her
at Gwytherin himself in November AD 660. He died on 13th
June, probably in the late AD 660s or early 670s.